Heater system for microwave antennas



May 18, 1954 E. DYKE EI'AL 2,679,003

HEATER SYSTEM FOR MICROWAVE ANTENNAS Filed- May 27. 1950 4 Sheets-Sheet1 FIG. I

IN V EN TOR.

. Edwin Dyke Q BY Richard Y. Hoffman .Tr.

May 18, 1954 E. DYKE ET AL 4 Sheets-Sheet 2 Filed May 27, 1950 INVENTOR.Edwin Dyke B Richard Y. Hoffman Jr.

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iiinw Q. W1 F M May 18 1954 E. DYKE ETAL HEATER SYSTEM FOR MICROWAVEANTENNAS 4 Sheets-Sheet 3 Filed May 27. 1950 Amplifier *ReceiverINVENTOR. Edwin Dyke Richard Y. Hoffman May 18, 1954 E. DYKE ETAL2,679,003

HEATER SYSTEM FOR MICROWAVE ANTENNAS Filed May 2'7, 1950 4 Sheet s-Sheet4 FIG. IO

TO AC SOURCE INVENTOR. Edwin Dyke BY Richard Y. HoffmunIr Patented May18, 1954 HEATER SYSTEM FOR MICROWAVE ANTENNAS Edwin Dyke, Brookfield,and Richard Y. Hoffman, Jr., Northbrook, Ill., assignors to Motorola,Inc., Chicago, 111., a corporation of Illinois Application May 27, 1950,Serial No. 164,818

17 Claims. 1

This invention relates generally to wave reflectors and moreparticularly to a heated reflector device for electrical microwaves forpreventing the collection of ice and snow thereon.

Various reflecting structures have been provided for directing waveswhich are transmitted from one point to another. These structures havereflecting surfaces which are generally parabolic and operate to convertthe waves from a small source into a parallel beam or conversely from abeam to a source. For electrical signalling at microwave frequenciessuch a reflector is used at the radiating and/or receiving antenna.

When such a reflector is used in the outdoors where it is exposed torain, snow, sleet and the like, ice and snow will form on the reflectingsurface and reduce the effectiveness thereof. Bhis is particularly truewhen the reflectors are mounted horizontally, as in such cases thereflector forms a container to hold the snow and water which freezes toform ice. Means for draining the reflector have been provided to removewater therefrom but such means are not effective when the temperature isbelow freezing so that the water forms ice on the reflector surface.Also, falling snow or sleet Will'adhere to the surface and reduce theefiectiveness thereof.

t is therefore an object of the present invention to provide an improvedreflector in which the accumulation of ice and snow on the reflectingsurface thereof is eliminated.

Another object of this invention is to provide an automatic heatingsystem for a horizontally positioned outdoor antenna reflector whichprevents the accumulation of ice and snow on the reflecting surfacethereof.

Still another object of this invention is to provide an automaticelectric heating system for an antenna reflector having a controlcircuit for energizing the system so that it utilizes a minimum ofpower.

A feature of this invention is the provision of a reflector having aparabolic reflecting surface and an elongated heating element positionedadjacent the back or convex surface thereof, with the heating elementbeing substantially uniformly positioned over the convex surface forheating the reflector.

A further feature of this invention is the provision of a horizontalmicrowave reflector having a drain for removing water therefrom and aheating element with portions adjacent the reflector and extendingwithin the drain for preventing the formation of ice and snow on thereflecting surface and for preventing the blocking of the drain due tothe freezing of water therein.

A still further feature of this invention is the provision of aspider-like structure for supporting one or more heater elements closelyadjacent the back side of a reflector.

Another feature of this invention is the provision of an automaticcontrol circuit for controlling one or more heating elements on areflector, with at least one of the elements being controlled by thetemperature about the reflector.

Another feature of this invention is the provision of a heating systemfor a reflector in which a first heating element is controlled by thetemperature about the reflector and a second heating element iscontrolled in accordance with a condition at the reflecting surface. Thesecond heating element may be controlled by the temperature on thereflecting surface, by the effectiveness of reflection surface inreflecting the waves, or by the actual presence of ice or snow on thereflecting surface.

Further objects and features and many advantages of the presentinvention will be apparent from a consideration of the followingdescription when taken in connection with the accompanying drawings inwhich:

Fig. 1 illustrates a microwave station using a reflector in accordancewith the invention;

Fig. 2 is a bottom view of the reflecting member with the heatingelement positioned thereon;

Fig. 3 is a perspective View, partly broken away, illustrating theconstruction of the reflector;

ig. 4 is a cross sectional view illustrating the mounting of the strapsfor supporting the heating elements;

Figs. 5 and 6 illustrate a modified supporting strap structure;

Fig. 7 illustrates a control system for a reflector heater includingmain and auxiliary heating elements;

Fig. 8 illustrates a heater control system having an element operated bythe reflection characteristics of the reflector;

Fig. 9 illustrates a heating system in which an auxiliary heater isenergized when ice or snow forms on the reflecting surface; and

Figs. 10 to 13 inclusive illustrate another embodiment of the systemincluding a device for detecting ice or snow.

In practicing the invention there is provided an antenna reflector whichis positioned horizontally to direct waves between an antenna and a flatreflector. The reflector has a concave parabolic reflecting surfacewhich is directed upwardly and a convex back surface on which theheating element is positioned. The heating system may be Wound in theform of a spiral and is positioned substantially uniformly over the areaof the reflector. A portion of a heating element extends in, andslightly beyond, the drain for the reflector so that ice and snow meltedby the heating element will have a free passage which does not becomeblocked by freezing of the water therein. It may also be desirable toprovide means for heating the end of the antenna horn to prevent thecollection of ice or snow thereon. Supporting structures includingstraps engaging the elongated heating element are provided forsupporting the heating element adjacent the convex back surface of thereflector.

The heating element may be made up of a 35. The other coil may beoperated by a separate control as for example by a control responsive tothe temperature of the reflecting surface itself. A control may also beprovided for an auxiliary coil which is operated in accordance with theoutput of the receiver associated with the reflector. The auxiliary coilwill be energized when the received signal falls below a predeterminedlevel indicating defective reflection. Another system which can be usedis to control a heating coil by the presence of ice and snow. Thepresence of ice and snow may be detected by heating a portion of thereflector or an adjacent surface to melt any ice or snow thereon. Thewater thus produced may be used to control the energization of a heatingcoil on the reflector.

Referring now to the drawings, in Fig. 1 there is illustrated amicrowave system including transmitting and/ or receiving equipment iiihaving an antenna H extending therefrom. A reflector I2 is provided fordirecting waves from the antenna ll toward a flat reflector l3. ReceivedWaves are also reflected by the flat reflectors it to th upwardly turnedparabolic reflector I2 and thereby directed to the antenna ll. As shownin Figs. 1 to 4 inclusive, the reflector includes a cup shaped member I5having an upwardly turned concave surface which is of parabolicconfiguration. A housing It of frusto-conical shape has a rim I! whichis secured to the rim it of the reflecting member IS. The housing l6 maybe supported on the microwave equipment It] by adjustable supports IE,or may be supported in any other suitable manner. An opening I9 isprovided in the cup shaped member l5 and an opening is provided in thehousing It through which the antenna 1! from the microwave equipmentextends.

Qpenings 2i and 22 are provided in the cup shaped member I5 and thehousing I6, respectively, at the center thereof, through which watercollecting in the reflector may be allowed to drain. A duct structure 23is provided for carrying this water to the side so that it does not flowdirectly on the housing for the microwave equipment !0. To prevent iceand snow from collecting on the reflector member 1 5, an elongatedheating element 25 is wound in the form of a spiral on the under side ofthe reflector member. As shown in Figs. 2 and 3, this heating elementextends from connector 26 to the edge of the reflector member andprogresses spirally inward to the center of the reflector member. Theheating element then continues down the drain and back in a hairpinshaped section with the end being returned to the connector 26.

The heating element is held in position against the under side of thereflector member by a spider like structure including a center ring 30and a plurality of straps 3| radiating therefrom. The straps aresupported at the edge [8 of the reflector member by a bolt and springassembly 32 which provides continuous tension for the straps. The boltsprovide adjustable tension for the straps. The straps therefor hold theheating element firmly against the deflecting member. Projections 33 maybe formed in the strap for locating the position of the various turns ofthe heating element against the reflector member so that the turns willnot slip clue to vibration of the member.

The straps 3| of the spider may alternatively be positioned directlyagainst the under surface of the reflector member 15 as shown in Figs. 5and 6. In this construction, punched out lugs 35 are provided which formprojections on which the heating element may be wound or positioned,with the lugs thereafter being bent over to securely hold the element inposition. In Fig. 5 the lug 35a is shown in the first position forwinding the heating element thereon, and the lug 35b is shown in theposition after it has been formed about the heating element 25. In sucha construction it may not be necessary to provide tensioning means forthe straps and they may be secured to the reflector by rivets asindicated at 31.

Energization of the heating coil 25 may be controlled by a thermostaticswitch 40 positioned within the housing I6. This switch is connectedthrough cable 4| to a source of energy and through conductors 42 to theconnector 26. The thermostatic switch 40 may be adjusted to connect theheating element 25 when the temperature of the reflector assemblyreaches any predetermined value. It has been found that the thermostaticswitch should be set to operate at about 35. Therefore, if rain or snowstrikes the reflector it will not freeze thereon and be retained butwill be melted and will naturally flow through the opening in the centerof the reflector member and through the duct structure 23 and willtherefor be removed from the reflector unit. The heating element inaddition to heating the surface of the reflector member also heats thedrain structure 23 so that a free path is provided for the Water to flowaway from the structure and the drain will not become blocked by frozenwater.

In Fig. 7 there is illustrated a control system which may be used withthe reflector heating system disclosed in the prior figures. In thissystem the heating element is divided into first and second coils orportions. The coil 5!! is connected to the power source throughthermostatic switch 5! which may be responsive to the temperature aboutthe reflector structure. Accordingly, when the temperature about thereflector reaches a predetermined value, as for example 35, the coil 59will be energized to heat the reflector member. The coil 52 is connectedto the source of power through the thermostatic switch 5| and a secondthermostatic switch 53 connected in series therewith. The thermostaticswitch 53 is positioned on the reflector surface and is responsive tothe temperature on the reflecting surface of the reflector member l5.This switch may also be set at 35 for example. Therefore, if the outsidetemperature is such that the coil is not effective to heat the reflectormember 15 to such an extent that the temperature of the refleetingsurface is 35 or more, the thermostatic switch 53 will close energizingthe coil 52. The two coils will therefore operate together to heat thereflecting member IE to a greater extent. Such a system provides therequired heating of the reflector member for wide changes in temperatureand yet is eiiicient in that only a part of the heating element isenergized when the temperature is such that this part will provide allthe heating that is necessary.

In Fig. 8 there is disclosed a further embodiment of the invention inwhich the heating element includes main and auxiliary heating coils orportions. The main coil 55 is connected through thermostatic switch 56which may be responsive to the temperature about the reflectorstructure. The auxiliary coil is also connected through the thermostaticswitch 56 and is also connected through a relay 58. The relay 58 may beconnected to the output of an amplifier 59 which is connected to theoutput of the limiter of the receiver 68. The output of the limiter ofthe receiver depends upon the strength of the signal received and whenthe limiter output is of such value that good reproduction of thereceiving signal is possible, the amplified limiter current will holdthe relay 58 open so that the coil 5'! is not energized. However, if theoutput of the limiter falls below this predetermined value, the relay 58will be deenergized and the coil 57 will be connected to the source ofpower to provide additional heating of the reflector member [5.

Therefore, if the snow or ice collects on the surface of the reflectormember l5 and the temperature is such that the snow or ice is notremoved by operation of the heating coil 55, the reflectioncharacteristics of the reflector member will be changed so that thereceived signal will be great- 1y attenuated. This will cause the relay58 to drop out so that the heater 5! is energized. When the receivedsignal is increased in strength due to the improved reflection, the coil5! will be deenergized. It is apparent from the above that this systemis highly economical of heater energy and the auxiliary coil 57 will beconnected only when necessary to provide the required signal level.

In Fig. 9 there is disclosed a still further system in which the heatingelement is formed by coils and 6'2. to a source of power throughthermostatic switch 5 and is positioned near the center of the reflectormember about the center opening therein. A second heating coil 67 isprovided extending from the first coil 55 to the edge of the reflector LThis second coil is connected to the member. source of power through thethermostatic switch t6 and also through a cell 68 which is in serieswith the switch and the coil 61. The cell includes a container cc havinga pair of electrodes positioned therein. The container 69 is placedbelow the opening 2! in the reflector member l5 so that any ice or snowon the reflector will be melted by heat from the coil 55, and the waterresulting therefrom will flow into the container 69 and provide ciosedcircuit between the electrodes lil. This will cause cnergization of thecoil 61 to heat the remainder of the reflector member. It is thereforeseen that when ice or snow is present on the reflector. and the coil 55is energized, the ice or snow will be melted causing the circuit throughthe coil Bl to be energized and the entire reflector member to bethereby heated. Since the coil is also connected through thethermostatic switch 65, the coil 61 will not be energized by thepresence of water alone as might be pro- The heating coil 65 isconnected duced by rain, when the temperature about the reflector isabove that at which the thermostatic switch 66 will be closed.

It may be preferable to provide the snow detector as a separate elementinstead of incorporating it with the antenna reflector itself. Such anarrangement is shown in Figs. 10 to 13 inclusive. In Fig. 10 thereflector member !5 is provided with a supporting housing to as in theembodiments previously described. A single heating coil 15 is providedon the rear surface of the reflector for heating the same. The coil '55is energized through. the contacts it of relay ll so that when the relay"H is energized the contacts i6 will close and the heating coil l5 willbe energized.

The relay H is part of an external snow detector device which is bestshown in Figs. 11 and 12. The device includes a cylindrical housinghaving a flat base 85 and a conical or funnel-shaped top 82. Within thehousing is a frame structure including the insulating members 83, 84 and85. Supported on the insulating member 33 is a heating coil 35. As shownin 10 this heating unit 3% is connected through the thermostat 8'!across an alternating current source so that when the temperature fallsbelow a predetermined value the thermostat 8'! will close and theheating unit as will be energized. The housing so is lined withinsulating material it to reduce the escape of heat through thecylindrical housing walls, and the heat therefore to heat thefunnelshaped member This is effective to melt any ice or snow which mayhave formed on the funnel-shaped surface 32.

As shown best in Fig. 13, a J-shaped trough 88 is placed below thecenter of the member 82 so that any water appearing on the surface 82 resulting from the melting of ice or snow is carried down the trough St tothe space between electrodes 88 and 923. The trough to serves as a windshield and serves to carry any drops from the funnel-shaped surface 32to the space between the electrodes 89 and st. The bottom wall 8!includes openings 55 therein to permit the escape of water therefrom.

As shown clearly in 19, the electrodes 89 and are connected in a seriescircuit across the A. C. source, which circuit includes rectifier 9!,resistor 92 and relay 93. The relay 93 is a very sensitive directcurrent relay which is actuated when a very small current is provideddue to the drops of water bridging the electrodes 89 and 90. It may bedesired to provide a coating on the surface 82 which will be partiydissolved by the water thereon and will render the water more conductingwhen it flows between the electrodes. The rectifier 9i may be of theselenium type and is connected in a peak rectifying circuit includingcondenser 9d. manner in which these elements are supported andpositioned in the housing is shown in Figs. 11 and 12.

The operation of the system of Figs. 10 to 13 inclusive is believed tobe clear from the foregoing description and from a consideration of MFig. 10. The detector must be located adjacent the reflector withsurface 32 positioned so that ice or snow will collect thereon under thesame conditions as on the reflector. The heater unit 85 is energized bythermostat 8? when the temperature falls below a predetermined value.The thermostat maybe set to energize the heater when the temperaturefalls below 35 F. as at higher temperatures than this snow or ice willnot form on the antenna reflector. The thermostatic switch 8'3 alsocloses the circuit through the rec tifler 9i, electrodes 89 and 90, andrelay 93, so that the relay 93 will be actuated in the event that thereis moisture on the surface 82 which flows between the electrodes 89 and80 to close the circuit therethrough. The relay 93 includes contacts 96which close to connect the heavy duty relay Tl across the alternatingcurrent source and this relay in turn connects the heating coil '15 onthe surface of the antenna reflector to the alternating current powersource.

It is seen from the above that there is provided a heating system forwave reflectors, such as is used in the transmission of microwaves,which is of relatively simple construction and which provides effectiveremoval of ice and snow from the reflecting surface. lhe heating systemmay be automatically controlled so that energy is consumed only whenheat is actually needed. As described above, this may be done in variousways. The heating element may include one portion which is controlled inaccordance with the temperature about the reflector, and a secondportion which is controlled in accordance with a condition on thereflecting surface, such as the temperature thereof, the efiiciency ofreflection, or the actual presence of ice or snow. The structure forsupporting the heating coils provides a secure mounting therefor and isadjustable so that the desired amount of tension can be provided. Theprovision of a section of the heating coil in the duct which forms adrain insures that the drain will remain open for removal of the meltedice and snow therefrom.

Although certain embodiments of the invention have been described whichare illustrative thereof, it is obvious that various changes andmodifications can be made therein without departing from the intendedscope of the invention as defined in the appended claims.

We claim:

1. An electric wave reflector system adapted to be installed out ofdoors including in combination, a cup shaped member having a concavereflecting surface and a convex back surface, an elongated heatingelement positioned in a spiral adjacent said back surface for heatingsaid member to remove ice and snow from said concave refleeting surface,and supporting means holding said element adjacent said convex backsurface, said supporting means including a central portion and radiallyextending strap portions connecting said central portion to the edge ofsaid cup shaped member, said strap portions including adjustabletensioning means for holding the same tensioned.

2. An electric wave reflector system adapted to be installed out ofdoors including in combination, a cup shaped member having a concavereflecting surface and a convex back surface, an elongated spirallywound heating element positioned adjacent said back surface for heatingsaid member to remove ice and snow from said concave reflecting surface,and supporting means holding said element against said back surface,said supporting means including a central member, strap membersextending radially therefrom and tension means securing said strap meansto the edge of said cup shaped member, said strap members holding saidheating element firmly against said back surface and having projectionsthereon for restraining lateral movement of said heating element.

3. An electric wave reflector system adapted to be installed out ofdoors including in combination, a cup shaped member having a concaverefleeting surface and a, convex back surface, an elongated heatingelement positioned adjacent said convex back surface for heating saidmember to remove ice and snow from said concave reflecting surface, andsupporting means holding said element against said back surface, saidsupporting means including a central portion and radially extendingstrap portions connecting said central portion to the edge of said cupshaped member, said strap portions having projections thereon engagingsaid heating element for supporting the same.

4. A wave reflector system including a cup shaped member having anupwardly extending concave reflecting surface and a convex back surface,said member having a central opening therein, duct means below saidopening forming a drain for liquid flowing through said opening, anelongated heating element having a portion positioned adjacent saidconvex back surface and being substantially uniformly positioned overthe area thereof, and a portion extending in said duct means, meanholding said element against said convex back surface, and means forenergizing said heating element including a thermal controlled switch.

5. A wave reflector system including a cup shaped member having anupwardly extending concave reflecting surface and a convex back surface,said member having an opening therein for the escape of water whichcollects therein, duct means adjacent said opening forming a drain forwater which flows through said opening, and an elongated heating elementhaving a portion positioned adjacent said back surface and a portionextending in said duct means, said heating element being effective toremove snow and ice from said reflecting surface and from said ductmeans.

6. A wave reflector system including a cup shaped member having anupwardly extending concave reflecting surface and a convex back surface,said member having a central opening therein, duct means adjacent saidopening forming a drain for water flowing through said opening, and anelongated heating element having a portion positioned adjacent saidconvex back surface and a portion extending in said duct means, saidheating element serving to prevent the collection of ice and snow onsaid reflecting surface and said duct means.

7. An electric wave reflector device including in combination, a cupshaped member having a concave reflecting surface and a convex backsurface, an elongated heating element positioned adjacent said convexback surface and being substantially uniformly positioned over the areathereof, said heating element having first and second portions andcontrol means for energizing said portions of said heating element, saidcontrol means including a thermal controlled switch for selectivelyenergizing said first heating element portion in accordance with thetemperature about said device and an auxiliary control for selectivelyenergizing said second heating element portion after said thermalcontrolled switch has been operated.

8. An electric wave reflector device including in combination, a cupshaped member having a concave reflecting surface and a convex backsurface, an elongated heating element positioned adjacent said convexback surface, said elements being substantially uniformly positionedover the area of said convex back surface, said heating elementincluding first and second portions and control means for energizingsaid heating element portions, said control means including a firstcontrol circuit for selectively energizing said first heating elementportion in accordance with the temperature about said device and asecond control for selectively energizing said second heating elementportion in response to a condition of said reflecting surface whichaffects the reflection characteristic thereof.

9. An electric wave reflector device including in combination, a cupshaped member having an upwardly extending concave reflecting surfaceand a convex back surface, duct means associated with said member fordraining water therefrom, an elongated heating element positionedadjacent said convex back surface, said heating element including firstand second portions with said first portion having a section thereofextending in said duct means, and control means for energizing saidheating element portions, said control means including a thermalcontrolled switch for energizing said first heating element portion inaccordance with the temperature about said device and an auxiliarycontrol for selectively energizing said second heating element portionafter said first heating element portion has been energized in responseto a condition of said reflecting surface which affects the reflectioncharacteristics thereof.

10. An electric wave reflector system including in combination, a cupshaped member having a concave reflecting surface and a convex backsurface, an elongated heating element positioned adjacent said convexback surface and being substantially uniformly positioned over the areathereof, said heating element including first and second portions, andcontrol means for energizing said heating element portions, said controlmeans including a first thermal controlled switch for selectivelyenergizing said first heating element portion in accordance with thetemperature about said device and a second thermal controlled switch forselectively energizing said second heating element portion in accordancewith the temperature of said reflecting surface.

11. An electric wave reflector system including in combination, a cupshaped member having a concave reflecting surface and a convex back surface and including means for draining moisture from said concavereflecting surface, a heating element positioned adjacent said convexback surface for heating said cup shaped member and preventing thecollection of ice and snow on said reflecting surface, said heatingelement including first and second portions with said first portionincluding a part for heating said draining means,

and control means for energizing said heating elements, said controlmeans including a first control circuit for selectively energizing saidfirst heating element portion in accordance with the temperature aboutsaid device and a second control circuit for selectively energizing saidsecond heating element portion in accordance with the temperature ofsaid reflecting surface.

12. An electric wave reflector system for reflecting waves to an antennawhich is connected to a receiver having a portion producing a signalvarying with the strength of the wave received by the antenna, saidsystem including in combination, a cup shaped member having a concavereflecting surface and a convex back surface, an elongated heatingelement positioned adjacent said convex surface and being substantiallyuniforml positioned over the area thereof, said heating elementincluding first and second portions, and control means for energizingsaid heating elements including a control circuit for selectivelyenergizing said first heating element portion in accordance with thetemperature about said device, and an auxiliary control circuit forselectively energizing said second heating element portion after saidfirst heating element portion has been energized, said auxiliary controlcircuit including relay means coupled to said receiver portion providingan open circuit when the signal therein exceeds a predetermined valueand providing a closed circuit when the signal therein falls below saidpredetermined value, so that said second h ating element portion isenergized when the signal in said receiver portion falls below saidpredetermined value.

13. An electric wave reflector system for reecting waves ta an antennawhich is connected to a receiver having a portion producing a signalvarying with the strength of the wave received by the antenna, saidsystem including in combination, an upwardly extending cup shaped memberhaving a concave reflecting surface and a convex back surface andincluding means for draining moisture from said concave reflectingsurface. an elongated heating element including first and secondportions positioned adjacent said convex surface for heating said cupshaped memher, said first heating element portion including a part forheating said draining means, and control means for energizing saidheating elements including a thermal controlled switch for energizingsaid first heating element portion in accordance with the temperatureabout said device, and auxiliary switching means for selectivelyenergizing said second heating element portion, said auxiliary switchingmeans being coupled to said receiver portion and providing an opencircuit when the signal therein exceeds a predetermined value and aclosed circuit when the signal therein falls below said predeterminedvalue.

14. An electric wave reflector device adapted to be installed out ofdoors including in combination, a cup shaped member having an upwardlyextending concave reflecting surface and a convex back surface, said cupshaped member including means for draining water therefrom, an elongatedheating element positioned adjacent said convex back surface and beingsubstantiall uniformly positioned over the area thereof, said heatingelement including a portion for heating said draining means, and controlmeans for energizing said heating element including a thermal controlledheating unit for heating an exposed surface portion in accordance withthe temperature about said device, and a control circuit includingspaced electrodes positioned to receive therebetween water drained fromsaid surface portion, to form a closed circuit for energizing saidheating element.

15. An electric wave reflector device adapted to be installed out ofdoors including in combination a cup shaped member having an upwardlyextending concave reflecting surface and a convex back surface, said cupshaped member having an opening therein and duct means connected theretofor draining water therefrom, an elongated heating element positionedadjacent said convex surface for preventing the collection of ice andsnow on said reflecting surface, said heating element having a firstportion positioned adjacent said opening and extending along said ductmeans and a second portion, and control means for energizing saidheating elements including a first control circuit for selectivelyenergizing said first heating element portion in accordance with thetemperature about said device, and an auxiliary control circuit forselectively energizing said second heating element portion after saidfirst heating element has been energized, said auxiliary control circuitincluding a container and spaced electrodes therein, said duct meansdirecting water from said opening into said container in contact withsaid electrodes for closing the circuit therethrough and energizing saidsecond heating element portion.

16. An electric wave reflector device adapted to be installed out ofdoors including in combination, a cup shaped member having an upwardlyextending concave reflecting surface and a convex back surface, said cupshaped member including means for draining water therefrom, an elongatedheating element positioned adjacent said convex back surface and beingsubstantially uniformly positioned over the area thereof and having aportion heating said draining means, and control means for energizingsaid heating element including means positioned adjacent said reflectingsurface for detecting the presence of ice or snow.

17. An electric wave reflector system adapted to be installed out ofdoors including in combination, a cup shaped member having a concavereflecting surface and a convex back surface and including means fordraining water from said concave reflecting surface, electric heatingmeans positioned adjacent said convex back surface and adapted to heatsaid surface substantially uniformly over the area thereof, said heatingmeans including a portion for heating said drain means, and temperatureresponsive means for controlling the energization of said heating means.

References Cited in the file of this patent UNITED STATES PATENTS

